In electronic componentry, in which switching processes are carried out with electric voltages or currents, interferences are generated as a consequence of these switching processes due to the generated electrical pulses with the associated emission of interference signals. These interferences can propagate as electromagnetic waves conductively across lines as well as also radiatively through free space.
The capability of a technical device not to subject other devices to unintentional or accidental electric or electromagnetic effects or be subjected to same by other devices, is referred to as electromagnetic compatibility (EMC).
To avoid or minimize the propagation of such interferences, prior art proposes equipping this componentry with a filter unit, a so-called EMC filter or network filter. It is also known to take measures for shielding or screening the electronic componentry in order to avoid impacting the correct functions of other electronic components or devices through interference signals of too high an amplitude level.
Such EMC filters are also utilized in hybrid and electric motor vehicles for example. The present description refers, in particular, to the use of EMC filters in electrical refrigerant compressors of motor vehicles in order to ensure that specified electromagnetic limit values are observed.
The magnitudes of such interference signals that must be observed by a device in circulation are established in EMC standardizations associated with this device and described by means of limit values that must be observed.
Known in this context are for example the so-called ECE provisions which include a catalog of international agreements on uniform technical regulations for motor vehicles as well as parts and equipment objects of motor vehicles. The area of radio interference suppression is treated, for example, in ECE R10, which has to be followed in future developments and which will result in further decrease of the permissible interference radiation.
Electromagnetic interference radiation is also generated in the operation of electric inverters that actuate an electric motor and thus switch currents of high amplitude. Such an inverter is utilized, for example, in actuating a motor in an air conditioner compressor of a motor vehicle.
A known solution for suppressing the interference radiation on electric or electronic components is the use of a passive EMC filter which is inserted, for example, in a feed line of the operating voltage. Such passive EMC filters are conventionally realized with the aid of passive components such as capacitors, coils and resistors which are connected in known, suitable manner and consequently generate the desired filter effect.
Based on the type of interferences to be filtered by means of an EMC filter, the distinction is made between common mode interference and differential mode interference. The interference spectrum to be filtered by the EMC filter is in practice comprised of the sum of both superposed interference components.
The type, structure and especially the voltage level of an inverter, for example for an electric refrigerant compressor, determine which of the two interference components is predominant and, consequently, which of the two interference components must be filtered more strongly.
In the case of inverters for refrigerant compressors that are operated in a voltage range of approximately 48 V, primarily differential mode interferences occur due to the low operating voltage and the simultaneously high arising currents in a range of, for example, 100 A to 200 A.
Prior art proposes filtering such differential mode interferences by employing so-called chokes in combination with capacitors in a passive EMC filter. For this purpose, for example, in each feed line of the inverters HV+ and HV− one choke L1 and L2 each is inserted and corresponding capacitors C1 and C2 are disposed in feed lines HV+ and HV− before and after the chokes L1 and L2. In addition, in passive EMC filters a third capacitor C3 is connected between the input line HV− and ground potential and a fourth capacitor C4 between the input line HV+ and ground potential.
Chokes as coils or inductors are known for limiting currents in electric lines, for the intermediate storage of energy in the form of their magnetic field, for impedance matching or for filtering. Such chokes are frequently inserted into a voltage feed line of an electric component. To enhance their so-called inductive reactance or reactance, chokes frequently include a soft magnetic core. It is known to utilize as the soft magnetic materials ferromagnetic substances that can be readily magnetized in a magnetic field.
Through the chokes L1 and L2, disposed in the feed lines HV+ and HV− of the inverter, flows the maximally possible input current of the inverter which can be in the range of 150 A and more, and these chokes must consequently be appropriately dimensioned for this current load.
This high interference-superimposed input current engenders in chokes L1 and L2 a magnetic field. In contrast to so-called common mode chokes, in which, due to the counter directed windings of the two choke windings disposed on a common core the magnetic fields of the input currents in the common core cancel each other out, this positive effect does not occur in the case of differential mode chokes.
It is therefore technically not sensible to construct differential mode chokes, or chokes with which differential mode interferences are to be reduced, with their windings on a common core since the magnetic fields of both windings in the core are superimposed and so-called saturation effects occur earlier in such a configuration.
Due to the relatively high input currents in a range equal to or greater than 150 A at an operating voltage of, for example, 48 V, in the cores of the chokes or differential mode chokes considerable core losses occur with a power loss of several watt. These losses are determined by the properties of the core material utilized and the winding structure.
This power loss leads to heating of the core of the chokes whereby, in turn, the core properties are changed. It is especially disadvantageous that with the heating of a ferrite core its magnetic properties change such that the maximal flux density decreases before the occurrence of saturation effects.
According to prior art it is customary to operate, for example, a ferrite core of a choke of a passive EMC filter without a cooling system. Due to the heating, the components of such an EMC filter, especially the choke, are overdesigned in order to ensure reliable, interference free operation of the inverter as well as other componentries in the proximity of the inverter.
It can, alternatively, also be provided that air is conducted through the core of a choke or of a transformer, which is also referred to as active air cooling.
It is, in addition, also known to move a coolant through the core of a choke or a transformer, which is also referred to as active liquid cooling.
In the field of power electronics there is a trend toward higher power densities. In order to be able to achieve these increased power densities, the systems need to be designed optimally with respect to topology and semiconductor selection. Furthermore, the installation volume of the components is to be decreased. However, the decreasing volume in connection with a reduced surface impedes the possibilities for adequate cooling of such components.
A solution for cooling such components is found in the document “Cooling Concepts for High Power Density Magnetic Devices” by J. Biela and J. W. Kolar at http://www.pes.ee.ethz.ch/uploads/tx_ethpublications/biela_PCC07.pdf which consists in utilizing a heat pipe as heat exchanger, wherein the heat pipe, utilizing the heat of evaporation of a medium, can transport a heat quantity, for example, from a first end of the heat pipe to its second end.
However, such cooling methods can only be implemented in an electric refrigerant compressor of a vehicle, such as for example a motor vehicle, using technically complex and installation and cost intensive means.